This invention relates to apparatus for and a method of modelling which may be referred to as rapid modelling. It particularly relates to modelling using laminations of sheet material built up to produce a finished three-dimensional shape.
The technique of modelling using laminated sheet material is generally known and referred to as LOM (Laminated Object Manufacturing). Reference may be made to EP-B-272 305 of Feygin for general information.
In the known apparatus used for LOM, a roll of resin-impregnated paper is fed to lie horizontally on a support platform and ironed in place using a hot roller. A laser is used to trace the outline of a thin section of the object to be formed. The laser also traces a grid of break-lines in the portions of the paper sheet which will not be required for the finished object. Another sheet of paper from the roll is then fed onto the support platform, ironed in place and laser cut, the shape of the section being altered as required to comply with computer-generated instructions. Ultimately, a solid object will be built up from the paper layers, effectively incorporated in a solid body of paper laminations. The scrap is cut or broken away using the laser-cut break-lines, to reveal the object.
Although this technique has many potential uses, it is intended for making objects of a durable nature, for example prototypes, visualisation models for new designs, or moulds for short-run moulding.
There is a need for rapid manufacturing of objects which are not necessarily intended to be durable in the same way as laminated paper models produced hitherto. For example, casting of metals often requires the use of sacrificial mould patterns or cores which are currently made by machining polystyrene foam (or other synthetic foam materials) to produce the required three-dimensional shape. When the molten metal is to be cast, the pattern is used to form a sand-mould and the molten metal vaporises the foam. Machining, particularly of a large-sized sacrificial pattern, is expensive and requires setting up of machines for each pattern. Since the pattern cannot be recovered after use, a cheaper and more flexible manufacturing process for sacrificial patterns would be desirable.
Hitherto, no satisfactory means of adapting LOM techniques has been found to operate with foams or cellular materials in general. It will be appreciated that the texture of a synthetic foam is not homogeneous, because the sizes and shapes of the individual bubbles or cells in the foam cannot usually be controlled with any accuracy and nor can the way in which the bubbles or cells pack together and coalesce.
One object of the present invention to provide an apparatus for modelling using cellular structure sheet material, and also a method of modelling.
According to the invention there is provided modelling apparatus comprising:
(a) a support platform or table adapted to be incrementally raised and lowered in response to a predetermined program;
(b) a sheet feed mechanism for feeding cellular structure sheet material onto or over the support platform;
(c) a superstructure mounted over said support platform;
(d) cutting means movably mounted on said superstructure for cutting said sheet material to a predetermined depth and for positioned movement relative thereto and as determined by a said predetermined program so that a resulting cut out portion or portions from the sheet material remains or remain on the support platform;
(e) adhesive applicator means operable over said support platform for applying adhesive to said cut out portion or portions of said sheet material and as determined by a said predetermined program;
(f) and control means including input means for input of information concerning the desired size and shape of the model to be made and output control means for controlling the sheet feed mechanism and the movement of said support platform and of the cutting means and of the adhesive applicator means in accordance with a said predetermined program.
Preferably, the sheet feed mechanism comprises a pair of rollers, namely a feed roller having a roll of cellular structure sheet material thereon, and a take-off roller adapted to receive and roll up the apertured scrap cellular structure sheet material after cutting. The pair of rollers may have tension control means adapted to maintain sufficient tension in the cellular structure sheet material to maintain it in a flat condition on the support platform.
The cutting means may be mounted on carriage means movable on the superstructure in two orthogonal directions for co-ordinated positioning movement of the cutting means. The adhesive applicator means may be similarly mounted e.g., with the cutting means.
A travelling smoothing device may be provided on the superstructure, for example a brush, squeegee or roller for smoothing down further fed cellular structure sheet material against an adhesively coated underlying cut out portion or portions.
The cutting means may comprise a laser. Alternatively, it may comprise a plasma cutter, a solvent cutter or a hot wire cutter. The cutting means is preferably mounted vertically, at right angles to the support platform and is arranged to give a cut of predetermined depth equal to the thickness of the cellular structure sheet material.
The adhesive applicator means may be a hot melt adhesive sprayer.
Means may be provided for locating a cut out portion or portions, as initially cut from the sheet material, on the support platform to prevent displacement thereon from the required position.
Viewed from another aspect, the invention provides a method of modelling comprising the steps of:
(i) providing a support platform or table adapted to be incrementally raised and lowered in response to a predetermined program;
(ii) feeding cellular structure sheet material onto the support platform;
(iii) cutting said sheet material for its full depth and at positions determined by said predetermined program so that a cut out portion or portions from the sheet material remains or remain on the support platform;
(iv) applying adhesive to the cut out portion or portions from said sheet material at positions determined by said predetermined program;
(v) incrementally lowering the support platform so that the cut out portion or portions of cellular structure sheet material thereon is or are lowered from the remainder of the cellular structure sheet material;
(vi) feeding further cellular structure sheet material over the support platform and previously cut out portion or portions thereon;
(vii) incrementally raising the support platform so that said cut out portion or portions abut the underside of said further cellular structure sheet material;
(viii) causing or allowing the adhesive to secure the further cellular structure sheet material to the cut out portion or portions underlying it;
(ix) cutting said further cellular structure sheet material for substantially its full depth, without cutting the underlying cut out portion or portions; and repeating steps (iv) to (ix) until the desired model has been completed.
Step (viii) may comprise smoothing the further cellular structure sheet material with a travelling smoothing device against the underlying adhesively coated cut out portion or portions for ensuring adhesion thereto.
As a final step, any internal portions of the model to which no adhesive has been applied may be broken out of the model or otherwise removed.
The cellular structure sheet material may comprise polystyrene foam and may be in the form of sheets of between 3 mm and 10 mm in thickness and preferably about 3 mm to 5 mm thick. The sheet material may be sufficiently flexible for providing on a roll or may be more rigid, in which latter case individual sheets may be fed using a sheet feeder for example a suction i.e., vacuum feeder or a gravity-operated hopper feed.
Alternatively, the cellular structure sheet material may comprise urea formaldehyde foam, polyurethane foam or other rigid or semi-rigid structurally stable foam, material, with or without fillers or fibre additives. Alternatively the cellular structure sheet material may be a naturally occurring cellular material such as wood or cork.